This invention relates to a process for producing L-threonine using a microorganism belonging to the genus Escherichia and having resistance to rifampicin, lysine, methionine, aspartic acid and homoserine and an ability to produce L-threonine. L-threonine is not only useful as medicaments such as amino acid preparation, etc., but also utilizable as an additive for animal feed.
Heretofore, various processes for producing L-threonine by fermentation have been known; for example, a process using a microorganism belonging to the genus Escherichia and having a borrelidin sensitivity (Japanese Published Examined Patent Application No. 6752/76), a process using a microorganism belonging to the genus Escherichia which requires diaminopimelic acid and methionine for growth and of which threonine biosynthesis system is resistant to the feedback inhibition of threonine (Japanese Published Examined Patent Application No. 10037/81), a process using a microorganism belonging to the genus Serratia which is deficient in threonine dehydrogenase and resistant to threonine metabolic antagonist (Japanese Published Examined Patent Application No. 48195/77), a process using a microorganism belonging to the genus Corynebacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine, and a requirement for methionine (Japanese Published Unexamined Patent Application No. 19087/72), a process using a microorganism belonging to the genus Brevibacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine and a requirement for leucine (Japanese Published Unexamined Patent Application No. 31093/75), a process using a microorganism belonging to the genus Brevibacterium and having resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine and requirements for L-isoleucine and L-lysine (Japanese Published Unexamined Patent Application No. 224684/83), etc.